The invention relates to a process for monitoring objects, such as especially tools, or process areas, and a device for implementing the process.
It is known from the DE 30 03 431 C2 to monitor tools at machine tools, e.g. drills, by means of a feeler pin. The feeler pin is pivoted against the tool between the work cycles in order to check its presence and operativeness. The feeler pin sits on a shaft driven by an electric motor. The pivot angle of the feeler pin is defined by a shaft encoder. In an initialization and learning cycle (hereinafter referred to as a "teach-in" cycle) the feeler pin is pivoted against a reference stop, e.g. against an object to be monitored, whereby the angular position of this reference stop is stored as the desired angular value in a microcomputer. In the next monitoring cycle the pivot angle of the feeler pin that is determined by the shaft encoder is defined and the actual angular value, at which the feeler pin strikes the object to be monitored is compared with the stored desired angular value. If the two values agree, a good message is sent; if they deviate, a fault message is sent. If the device is used for monitoring a process area (free space monitoring), the good message is sent when the feeler pin can pass over the angular range of the process area. A fault message is sent, when the feeler pin strikes an impediment in the process area.
In the case of the prior art monitoring operation, the zero position of the feeler pin is fixed by a mechanical zero stop. The pivoting angle of the feeler pin is counted by means of the shaft encoder from this zero stop. When the feeler pin strikes the object to be monitored or the end of the process area, the electric motor's direction of rotation is reversed, e.g. by reversing the polarity of the d.c. electric motor that is used in order to swing the feeler pin back again into the zero position.
In the known device the feeler pin can be pivoted from the zero position only in one direction of rotation. The respective polarity of the electric motor gives the information concerning the pivoting direction of the feeler pin. Thus, the possible applications of the device are limited. When the feeler pin is reset into the zero position, the mechanical zero stop is approached. The associated mechanical stress affects the lifespan of the device.